Inside a motor vehicle, there is provided an air filter having a dust filter, an antibacterial filter and the like combined to keep indoor air comfortable. However, the air already introduced into a motor vehicle through a ventilation system or a heater is not easily discharged to the outside. The concentration of carbon dioxide inside the vehicle is higher than the concentration of carbon dioxide outside the vehicle due to the driver's breathing in a narrow indoor environment.
If a driver continuously inhales uncomfortable indoor air with a high concentration of carbon dioxide, the driver's body rhythm may be decreased, thereby causing drowsy driving.